pulsatile secretion
Pulsatile secretion means a hormone is released in discrete bursts — sharp spikes separated by quiet intervals — rather than poured out at a constant rate. It is the difference between a drummer keeping a beat and a steady hum. For several key hormones the rhythm of the beats carries information that a smooth steady level could not.
The clearest example is GnRH from the hypothalamus, which is released roughly once an hour. The frequency of these pulses is itself a signal: faster GnRH pulses favor LH secretion, while slower pulses favor FSH. Growth hormone, ACTH, and insulin are also secreted in pulses, and pulsatility helps keep receptors from becoming desensitized to a constant signal.
This frequency code has a striking clinical twist. Giving GnRH in natural-like pulses can restore fertility in some patients, but giving the very same hormone continuously does the opposite — it shuts the gonadal axis down. Long-acting GnRH analogs exploit this paradox to deliberately suppress sex hormone production in conditions such as prostate cancer and precocious puberty.
Continuous GnRH from a long-acting analog first briefly stimulates, then desensitizes the pituitary and suppresses LH and FSH — the basis for using these drugs to halt precocious puberty.
Pulses stimulate the gonadal axis; the identical hormone given continuously suppresses it.
Because hormones are secreted in pulses, a single blood measurement can land on a peak or a trough; this is why some hormones are sampled multiple times or assessed by dynamic testing.